A path configuration of a conventional TOC meter is shown in FIG. 6.
A syringe pump 4 is connected to a common port of a multi-port valve 2, and also, a tube for collecting a sample, dilute water or acid, a combustion tube 6, a pure water trap 10 or the like are connected respectively to other ports to be switched and connected to the common port. A path from a carrier gas supply unit 100 is connected to the syringe pump 4 via a three-way electromagnetic valve 34.
Sample water collected by the syringe pump 4 is injected into a sample injection unit 6a at an upper portion of the combustion tube 6 after carbon dioxide gas has been removed inside the syringe pump 4. The sample water injected into the sample injection unit 6a of the combustion tube 6 is supplied from the carrier gas supply unit 100 and guided inside the combustion tube 6 by a humidified carrier gas, and is combusted under the presence of a catalyst inside the combustion tube 6, and carbon components included in the sample water is thereby converted into carbon dioxide.
The gas (carbon dioxide and water vapor) generated in the combustion tube 6 is cooled in a cooling tube 8, and the carbon dioxide is guided into a dehumidification electronic cooler 36 via the pure water trap 10 to have water further removed, has halogen components removed by a halogen scrubber 40, is filtered by a membrane filter 42, and is introduced into a sample cell 44. Then, infrared light from a light source 46 is applied into the sample cell 44, and a signal which is proportional to the carbon dioxide concentration is obtained from a detector 48. Carbon dioxide discharged from the sample cell 44 is adsorbed by a CO2 absorber 50.
The carrier gas supply unit 100 includes, in order from the side of a carrier gas inlet, an electromagnetic valve 102, a pressure adjustment valve 104, a pressure sensor 106, a mass flow controller 108, and a flow meter 110, and is configured in such a way that after a measurer has set, before starting measurement, the pressure and the flow rate of a path through which a carrier gas is to be supplied to be predetermined values, the pressure and the flow rate are maintained to be constant. Carrier gas supply units of conventional TOC meters generally have the same configuration (for example, see Patent Document 1).
The path on the downstream side of the carrier gas supply unit 100 is separated into a path connected to the sample injection unit 6a of the combustion tube 6 and a path connected to the switching valve 34, and the carrier gas flows through both paths at a constant proportion at any time. For example, if the amount of supply is set at 230 mL/min for the carrier gas supply unit 100, the carrier gas flows to the side of the combustion tube 6 at 150 mL/min, and to the side of the switching valve 34 at 80 mL/min. The carrier gas flowing to the side of the switching valve 34 is introduced into the syringe pump 4 by the switching valve 34, or joins the carrier gas that is introduced into the sample cell 44 via the combustion tube 6. The carrier gas which has been introduced into the syringe pump 4 is used as a sparge gas for removing IC (inorganic carbon) in the sample water which has been drawn into the syringe pump 4.